Classification and cladistics

• Clade


  Group of organisms that have all evolved from a common ancestor
• Clades


  • Characteristics can be predicted using clades
• Cladogram


  Tree diagrams that show divergence of clades
• Creating cladograms

  1. Usually uses base sequences of genes/amino acids, although morphology can also be used

  2. Nodes occur when two or more species diverge (branch point)

  3. A root is the beginning

  4. A terminal branch is the end
• Molecular clock


  • Method of estimating times by looking at differences in DNA sequences
  • Mutations accumulate gradually at a constant rate
• Parsimony analysis


  • Used to select the most probable cladogram by accounting for observed sequence variation between clades with the smallest number of sequence changes
  • Assumes simplest hypothesis is the most likely
• Figworts


  • Classified using morphology, then reclassified using cladistics and genetic analysis of chloroplasts
  • Over half were reclassified
• Scientific knowledge can be falsified
• Three domains of life

  • Archaea, bacteria, eukaryotes
  • Archaea and eukaryotes have a more recent common ancestor
• Bacteria


  • Circular chromosome
  • No proteins with DNA
  • Sometimes introns
  • Peptidoglycan cell wall
  • No nucleus
  • Ester in plasma membrane
  • No extreme environment
• Archaea


  • Circular chromosome
  • Proteins with DNA
  • Usually introns
  • No peptidoglycan cell wall
  • No nucleus
  • Ether in plasma membrane
  • Extreme environment
• Eukaryotes


  • Linear chromosome
  • Histones
  • Always introns
  • Cellulose and chitin cell walls
  • Nucleus
  • Ester in plasma membrane
  • No extreme environment